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January Clearance 2017

Oversampling

From inSync reader Tom K: “I have heard about oversampling, and that it improves sound quality. But what exactly is going on, and what exactly is improved? Also, when is oversampling used? During recording or during playback? What’s the difference between 32x, 64x, 128x, etc. oversampling?”

Tom, this is a fairly deep subject! Here are reasonably brief answers to your questions: Oversampling is used during the analog to digital (A/D) and digital to analog (D/A) conversion processes in a digital recorder, sampler or playback device. Essentially, the sampling rate of the converter is multiplied to a very high rate (i.e. 4x oversampling puts the rate at 176.4 kHz). This accomplishes two things: First, it allows the anti-aliasing and anti-imaging filters on the converters to be much more gentle, which reduces phase distortion. Second, in a 4x oversampled system, it results in a 6 dB drop in noise (other rates result in more or less noise reduction).

Tom continues, “I was talking with a co-worker about digital audio, and I told him that all audio CD’s are in 44.1khz 16-bit stereo digital format, and if copied digitally, the audio will be identical when copied back to another CD… but he brought up oversampling, and said that if a CD is recorded with oversampling, a copy of this CD will be worse quality. What’s the deal?”

In this case, your co-worker is incorrect (don’t rub it in too much!). The data stored on a standard Red Book audio CD is 16-bits, at 44.1 kHz. While oversampling might result in a better A/D conversion when making the CD master, and an oversampling CD player might result in better D/A playback, this is a function of the converters, not the data on the CD. Digitally “cloning” that CD will produce an exact bit-for-bit copy. Since no conversion to analog is used, oversampling does not enter into the picture.

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